In the manufacture of semiconductor devices, ion implantation is used to dope semiconductors with impurities or dopants. Ion beam implanters are used to impact silicon wafers with an ion beam, in order to produce n or p type extrinsic material doping or to form passivation layers during fabrication of an integrated circuit. When used for doping semiconductors, the ion beam implanter injects a selected extrinsic ion species to produce the desired semiconducting material. Referring initially to prior art FIG. 1 is a conventional ion implantation system 100. Implanting ions generated from source materials such as antimony, arsenic or phosphorus results in “n type” extrinsic material wafers, whereas if “p type” extrinsic material wafers are desired, ions generated with source materials such as boron, or indium may be implanted.
An ion source 102 for producing an (e.g., a pencil ion beam, a ribbon-shaped, etc.) ion beam 104 along a longitudinal beam path 106. The ion beam source 102 includes a plasma source with an associated power source and an extraction apparatus 110, which may be of any design by which the ion beam 104 is extracted, for example. The following examples are provided to more fully illustrate the invention, but are not to be construed as limiting the scope thereof. For instance, the plasma source may comprise a relatively long plasma confinement chamber from which the ion beam 104 can be extracted using an extraction opening in the extraction apparatus 110. The formation of pencil, ribbon and other type ion beams is well known by those of skill in the art.
To produce the ions, a gas of a dopant material (not shown) to be ionized is located within a plasma chamber of the ion beam source 102. The dopant gas can, for example, be fed into the plasma chamber from a gas source (not shown). In addition to a power supply, it will be appreciated that any number of suitable mechanisms (none of which are shown) can be used to excite free electrons within an ion generation chamber, such as RF or microwave excitation sources, electron beam injection sources, electromagnetic sources and/or a cathode which creates an arc discharge within the chamber, for example. The excited electrons collide with the dopant gas molecules and ions are generated therein. Typically, positive ions are generated although the disclosure herein is applicable to systems wherein negative ions are generated as well.
The ions are controllably extracted through the extraction apparatus 110 in the ion beam source 102 by an ion extraction assembly (not shown), in this example. The ion extraction assembly can comprise a plurality of extraction, ground and suppression electrodes. The extraction assembly can include, for example, a separate extraction power supply (not shown) to bias the extraction and/or suppression electrodes to accelerate the ions from the ion source 102. It can be appreciated that since the ion beam 104 comprises like charged particles, the beam 104 may have a tendency to blow up or expand radially outwardly as the like charged particles repel one another. It can also be appreciated that beam blow up can be exacerbated in low energy, high current beams where many like charged particles (e.g., high current) are moving in the same direction relatively slowly (e.g., low energy) such that there is an abundance of repulsive forces among the particles, but little particle momentum to keep the particles moving in the direction of the beam path 106. Accordingly, the extraction assembly 110 is generally configured so that the beam 104 is extracted at a high energy so that the beam 104 does not blow up (e.g., so that the particles have sufficient momentum to overcome repulsive forces that can lead to beam blow up). Moreover, the beam 104, in this example, is generally transferred at a relatively high energy throughout the system and is reduced just before impacting with the workpiece 116 to promote beam containment.
A beamline system 112 is provided downstream of the ion source 102 to receive the beam 104 therefrom, comprising a mass analyzer 114 positioned along the path to receive the beam 104. The mass analyzer 108 operates to provide a magnetic field across the path so as to deflect ions from the ion beam 104 at varying trajectories according to mass (e.g., charge to mass ratio) in order to provide a mass analyzed ion beam 104 as illustrated in FIG. 1. The mass analyzer 114 therefore performs mass analysis and angle correction/adjustment on the ion beam 104. The mass analyzer 114, in this example, is formed at about a ninety degree angle and comprises one or more magnets (not shown) that serve to establish a (dipole) magnetic field therein. As the beam 104 enters the mass analyzer 114, it is correspondingly bent by the magnetic field such that ions of an inappropriate charge-to-mass ratio are rejected. More particularly, ions having too great or too small a charge-to-mass ratio are deflected into side walls of the mass analyzer 114. In this manner, the mass analyzer 114 merely allows those ions in the beam 104 which have the desired charge-to-mass ratio to pass therethrough and exit through a resolving aperture 116 of the resolving aperture electrode assembly 120.
The mass analyzer 114 can perform angle corrections on the ion beam 104 by controlling or adjusting the amplitude of the magnetic dipole field. This adjustment of the magnetic field causes selected ions having the desired/selected charge-to-mass ratio to travel along a different or altered path. The resolving aperture electrode assembly 110 is located downstream of the mass analyzer component 114 and along the beam path. A resolving aperture electrode assembly 116 has a size and shape according to a selected mass resolution and a beam envelope of the ion beam 104.
One or more deceleration electrodes 118 can located downstream of the ion beam deflecting component. The deceleration electrodes can be directly utilized for a high-current, ultra-low energy ion implanter to enable a high-current ion beam to be generated with ultra-low energy and with reduced energy contamination. Up to this point in the system 100, the beam 104 is generally transported at a relatively high energy level to mitigate the propensity for beam blow up, which is well known in the art, which can be particularly high where beam density is elevated such as at a scan vertex, for example. The deceleration electrodes comprise one or more electrodes operable to decelerate the beam 104. The electrodes typically contain apertures thru which the beam 104 travels.
Nevertheless, it will be appreciated that while deceleration electrodes 118 are respectively illustrated in the exemplary system 100, as parallel and with the apertures in the same plane, that these electrodes may comprise any suitable number of electrodes arranged and biased to accelerate and/or decelerate ions, as well as to focus, bend, deflect, converge, diverge, scan, parallelize and/or decontaminate the ion beam 104 such as provided in U.S. Pat. No. 6,441,382 to Huang et al., the entirety of which is hereby incorporated by reference.
An end station 108 is provided in the system 100, which receives the mass analyzed ion beam 104 from the beamline system 112 and supports one or more workpieces 110 such as semiconductor wafers along the path for implantation using the final mass analyzed ion beam 122. The end station 108 includes a target scanning system 126 for translating or scanning one or more target workpieces 110 and the ion beam 104 relative to one another. The target scanning system 126 may provide for batch or serial implantation.
It will be appreciated that ion beam collisions with other particles in the system 100 can degrade beam integrity. Accordingly, one or more pumps (not shown) may be included to evacuate, at least, the beamguide and the mass analyzer 114.
Typical ion implantation systems include an ion source 102 for generating positively charged ions from ionizable source materials. The generated ions are formed into an ion beam 104 and are directed along a predetermined beam path 106 to an implantation end station 108. The ion implantation system 100 may include beam forming and shaping structures extending between the ion source 102 and the implantation end station 108. The beam forming and shaping structures maintain the ion beam 104 and bound an elongated interior cavity or passageway through which the beam passes en route to the implantation end station 108. When operating an implanter, this passageway is evacuated to reduce the probability of ions being deflected from the predetermined beam path 106 as a result of collisions with gas molecules.
Trajectories of charged particles of given kinetic energy in a magnetic field will differ for different masses (or charge-to-mass ratios) of these particles. Therefore, the part of an extracted ion beam 104 which reaches a desired area of a semiconductor workpiece 110 or other target after passing through a constant magnetic field can be made relatively pure since ions of undesirable molecular weight will be deflected to positions away from the beam 104 and implantation of other than desired materials can be avoided. The process of selectively separating ions of desired and undesired charge-to-mass ratios is known as mass analysis. The mass analyzer 114 typically employs a mass analysis magnet creating a dipole magnetic field to deflect various ions in the ion beam 104 via magnetic deflection in an arcuate passageway which will effectively separate ions of different charge-to-mass ratios.
For some ion implantation systems, the physical size of the beam 104 is smaller than a target workpiece 116, so the beam is scanned in one or more directions in order to adequately cover a surface of the target workpiece 116. Generally, an electrostatic or magnetic based scanner scans the ion beam 104 in a fast direction and a mechanical device moves the target workpiece 116 in a slow scan direction in order to provide sufficient cover. The system can include a current density sensor, such as a Faraday cup 124, for example, that measures the current density of the scanned beam, where current density is a function of the angle of implantation (e.g., the relative orientation between the beam and the mechanical surface of the workpiece and/or the relative orientation between the beam and the crystalline lattice structure of the workpiece 116). The current density sensor moves in a generally orthogonal fashion relative to the scanned beam 104 and thus typically traverses the width of the beam 104. The dosimetry system, in one example, measures both beam density distribution and angular distribution.
For typical high current ion implantation systems various deceleration elements can reduce the energy contamination and increase the low energy beam current. (See e.g., U.S. Pat. No. 6,441,382 to Huang, the entirety of which is hereby incorporated by reference).
However, the implementation of deceleration elements into an ion implanter is strongly influenced by the architecture of that specific ion implanter. Therefore a system is needed that can achieve low particle contamination levels at low energies and can maintain the other performance requirement of the ion implanter.